Many fields require the switching of light to accomplish their task. One major application for the switching of light is in the field of computer data projection and television projection systems. Currently these products use either LCDs or MEMS mirror arrays to accomplish the task of switching light.
Another major industry that uses light switching technology is the communications market. In the communications field, switches are used to control light transmission to and from fiber optic cables.
Light valves are being used in more and more TVs and projection display systems. In TV applications the projector is often used in a rear projection configuration. For computer monitors using projection display, the front projection mode is more commonly used.
The MEMS mirror array type of light valve is disclosed in U.S. Pat. Nos. 4,566,935; 4,596,992; 4,615,595; 4,662,746; 4,710,732; 4,956,619; and 5,028,939; all by inventor Larry Hornbeck of Texas, and assigned to Texas Instruments (TI) of Texas. The TI patents are the foundation of the technology that is used by most manufacturers of TVs and computer projection displays. The TI technology uses an array of MEMS mirrors that change their incidence angle to the light path to switch the light from an off position to an on position. When the mirror is in the on position, the mirror reflects the light through the optical path. When the mirror is in the off position, the light is reflected to a path that falls outside the projection optics. This in effect turns the light valve to an off state.
There are many deficiencies with this technology. One is that the light transmission is less than 70%. To allow for the change of angular orientation of the mirrors, there must be a substantial space between adjacent mirrors. The required gap causes a lot of light to be wasted. Further, the reflected light is absorbed into the light valve. The absorbed energy makes cooling switching devices that use this technology a challenge.
Further, the high amount of absorption limits the amount of power that can be pushed through the light valve. This limitation either eliminates this type of device from being used in high power applications, or causes the necessity of a complex cooling solution.
Another shortcoming of devices using the TI technology is that the MEMS structure to create mirrors that can rotate is a complex one to manufacture.
Still another shortcoming in this technology is that the angle of deflection of the light is not precise. In some applications this lack of control over the angle to which the light is transmitted causes a further reduction of transmission efficiency.
Another popular technology for use in projection applications is LCD technology. However, LCDs are not efficient for the transmission of light. LCDs are slow in response time and do not work well at elevated temperatures. Because of their thermal limitations, the size of the LCDs must be much greater in size than competing technology devices.
Accordingly, it is an object of the present invention to provide a light valve with greatly improved efficiency.
It is another object of the present invention to provide a less complex light valve structure thereby making possible lower cost switching systems.
It is a further object to provide a light valve that reflects almost 100% of the light received, thereby enabling systems to run at extremely high powers while requiring less elaborate cooling systems than are required by current art systems.
It is a still further object of the invention to provide a light valve that can switch faster. This is because there is only a small movement in the MEMs elements during the switching.
It is yet another object of the present invention to provide a higher contrast ratio of the on state to the off state of the light valve.
It is a further object of the invention to provide a light valve that enables light to be accurately switched to two paths.